Problem : 10-5=?

- Let left = 10
- Let right = 5
- Let operator = - (subtraction)
- Solve for ?

Variables or identifiers

- Begin
- Declare x as an integer
- Declare y as an integer
- Declare z as an integer

In ram the "post box" contains x, z and y. All of them are in different containers

- Set x = 10
- Set y = 5

No in the "post boxes" x and y are equal to 10 and 5. X and y now point to the numbers they are supposed to represent.

- Set z = x-y (you substituted the numbers for their variables)
- Display x-y= z

We can now do another problem with the same variables

- P = Z * 2
- P is a null value
- It does not stand for anything

- P is a null value

P is now displayed as a null variable in RAM. When the computer solves the problem p then turns to point to 10.

- End the problem

**Terminology**

- Bin -
- Identifier in memory which points to a values

- Null -
- A thing with no value

**Contd.**

- Variables are stored in RAM as hexadecimal addresses.
- You have to always define the variables
- Integers always have a value
- An integers range is -2 147 483 684 to 2 147 483 647

- Integers always have a value
- For something to have a value in RAM it has to point to something
- Addresses have 16 digits
- In programming we are
- Mimicking real life objects in a computer environment
- People
- Buildings
- Cars
- Business Objects
- Money
- Working rates
- Tax

- Mimicking real life objects in a computer environment

Variables in Memory

- A address can only hold one variable
- When you add a new value to a variable it over-rides the original one.
- X=10
- X=20
- X=x+10
- X changes value every time here

- The equals sign represents an assignment operator
- The signs that we use
- +
- Addition

- -
- Subtraction

- *
- Multiplication

- /
- Division

- %
- Modulus
- The remainder of your division

- Modulus
- !
- Not

- =
- Assignment operator

- >=
- Greater than or equal to

- <=
- Less than or equal to

- ==
- Equality

- +

- When we manipulate x we manipulate the value in ram

Data Types

- Three common data types are used
- Integer
- Can store only whole numbers

- Floating point numbers
- Can store numbers with fractional values

- Character
- Can store a character

- String
- Character

- Integer
- Examples
- Age
- Integer

- Money
- Floating point

- Gender
- Character
- Alphanumeric

- Character
- Surname
- String
- De Beer

- Phone number
- String
- 011 465 7654

- String
- Date
- String
- 07/04/2015

- String

- Age

- If you are not going to use something in an expression, it is alphanumeric
- Strings are multiple character values
- When there is a single quotation mark it is a character
- When there are two quotation marks then it is a collection of characters
- Characters are for one character
- A bit is a 0 or 1
- One of them indicate on and the other off

- 8 bits make a byte
- 16 bits = 2 bytes
- 32 bits = 4 bytes
- 64 bits = 8 bytes